Inductive multi-speed resolver



Oct. 25, 1966 t B. P. BLASINGAME 3,281,655

INDUCTIVE MULTI SPEED RESOLVER Original Filed Oct. 8, 1959 PERMEABILITYSHAFT ANGLE 5 N E sin (w+- 42 I N VENTOR. 50A k 36/2 22/72/2/P/J705/23Q/222 ATTORNEY United States Patent 3,281,655 INDUCTIVE MULTl-SPEEDRESOLVER Benjamin I. Elasingame, 2621 E. Menlo Blvd, Milwaukee, Wis.

Original application Get. 8, 1959, Ser. No. 845,242, new Patent No.3,172,023, dated Mar. 2, 1965. Divided and this application Dec. 1,1964, Ser. No. 415,134

h Claims. (Cl. 323-51) This application is a division of copendingapplication Ser. No. 845,242, filed on Oct. 8, 1959, now US. Patent3,172,026, granted on March 2, 1965.

This invention relates to resolvers and more particularly to an improvedinductive-type resolver which provides an output related in phase to thedisposition of a magnetic body relative to a plurality of magneticpoles.

Present day resolvers are electromechanical devices which provide analternating current signal voltage whose phase dilfers from that of areference voltage by an amount precisely equal to the shaft rotation ofthe resolver. This action is accomplished by means of a four pole statorcontaining two field windings excited by voltages which are precisely 90out of electrical phase with respect to each other inside of which a twopole armature containing a single winding is rotated by the resolvershaft. This field arrangement is essentially analogous to that of a twophase induction motor wherein field windings are excited 90 out ofelectrical phase to produce a rotating magnetic field. The singlearmature winding of the resolver acts like the secondary of atransformer having induced in it the sum of voltages from both fieldwindings. The voltage induced by each field winding is porportional tothe sine of the angle between the axis of the armature and the axis ofthe field pole. Thus the armature voltage is given by the mathematicalexpression:

e =n e sin wl sin a+n e sin (wt-n/ 2) sin (a-11-/ 2) where: e =armaturevoltage magnitude. n =turns ratio of armature to pole number 1. e=voltage magnitude impressed on field number 1. w=frequency ofexcitation voltage in radians/sec. t=time in seconds. et=angle betweenaxis of armature winding and field pole number -1. n =turns ratio ofarmature to pole number 2. e =voltage magnitude impressed on fieldnumber 2.

Since the armature is rigidly hastened to the resolver shaft, or is alsothe angle of the resolver shaft with respect to the reference position.

This may be rewritten:

e n e sin wt sin an e cos wt cos a (1) If now n is made equal to 11 bymanufacture and e is made equal to e by the excitation provisions, thenapplying the formula cos (x+y) :cos x cos y-sin x sin y This may berewritten:

out in COS It is now seen that the output voltage is shifted inelectrical phase by exactly the shaft angle, a.

A device of this type has many uses in analogue :computations, datatransmission and general instrumentation applications. The phase shiftangle and hence shaft angle may be digitalized by suitable pulsecounting systems. Where a shaft position must be measured to extremeprecision, gearing is sometimes introduced between the shaft and theresolver. By gearing up the resolver, the phase angle can thus be madeto rotate through 360 electrical degrees for some fraction of a completerotation of the shaft. This introduces an ambiguity in the actual shaftposition which must be accounted for by some means such as anothersingle speed resolver. Such applications are common in the presentinstrumentation art.

Two problems in the use of resolvens are the inaccuracy, backlash andexpense introduced by gearing resolvers for high accuracy and theelectrical and mechanical problems attending the use of slip rings andbrushes to connect the armature windings to the resolver terminals. Theformer problem limits the accuracy of such systems to the accuracy ofgear trains and the latter limits the applications to environments whichare relatively free of vibration, corrosion, etc.

According to the present invention an inductive resolver or displacementmeasuring device is provided which produces an output related in phaseto the position of a relatively displaceable member, whichmember iscompletely free from windings there-on. In addition, the inventionprovides for a multi-speed inductive resolver which does not require theuse of a mechanical gearing With the difficulties attendant thereto. Ingeneral, this is accomplished by the provision of a plurality of salientmagnetic poles and magnetic flux return means spaced therefrom to definea plurality of flux gaps. Both primary and secondary windings areassociated with each of the poles so as to be linked magnetically to adegree dependent upon the orientation of a magnetic body which isdisplaceable through the gap relative to the poles. By exciting thevarious primary windings with voltages having predetermined phase angledifferences, a secondary voltage may be produced which is related inphase to the position of the magnetic body relative to the poles.

In a particular embodiment of the invention a multispeed inductiveresolver is provided which produces an output signal which varies inphase directly with displacement of a relatively movable body. Thisdisplacement phase characteristic may be accomplished by graduating thedimensions of the movable body such that the area of the movable bodywhich is presented to the adjacent poles varies approximatelysinusoidally with displacement of the body.

The present invention may be best understood by reference to thefollowing specification which describes two illustrative embodiments ofthe invention. These descriptions are to be taken with the accompanyingfigures of which:

FIGURE 1 is a cross-sectional view of a two-speed inductive resolver;

FIGURE 2 is a view of the end surface of the rotor of the inductiveresolver shown in FIGURE 1 and taken along a line 22 of FIGURE 1;

FIGURE 3 illustrates the variation of permeability in a representativeflux gap adjacent one of the poles when a rotor structure such as shownin FIGURE 2 is displaced thereby;

FIGURE 4 is a cross-sectional view of a linear displacement detectingdevice; and

FIGURE 5 is a sectional view of the displaceable body of the detectorshown in FIGURE 4 .and taken along a line 5-5 of FIGURE 4.

FIGURE 1 shows an enlarged sketch of an inductive multi-pole resolverfor which the name microsolver has been coined. This sketch shows a twospeed micro solverthe output voltage changes phase through 360electrical degrees while the shaft turns through This is the lowestspeed to which this design can be applied. On the other hand higherspeeds can be built the upper limit being fixed only by the allowableframe size and the practical limitations on the intricacy of the through8. Each pole carries two solenoid type windings one being a primary towhich the excitation voltage is applied and the other a secondary inwhich the output voltage is induced by transformer action. These polesand field windings are arranged in pairs, in the sketch the odd numberedpoles form one set of pairs which are all excited in phase with thereference voltage. Thus solenoid coils pairs 11 and 15 are connected inparallel to the reference excitation voltage source 20. Solenoid coilpairs 13 and 17 are connected in parallel and excited 90 electricaldegrees out of phase with the reference electrical voltage by quadraturevoltage source 22. Thus a rotating magnetic field is producedessentially as in the field of an induction motor. To do this, it isclear that the parallel connected solenoids are reversed in each pair sothat in reality coil pair 15 is excited 180 electrical degrees out ofphase with coil pair 11. Similarly coil pair 17 is excited 180electrical degrees out of phase with coil pair 13.

Consider now the function of the rotor 24 which is connected to andturned by shaft 26. The rotor is made of punched laminations, forexample, of high permeability magnetic material. The periphery of therotor makes a very large air gap with the field pieces except where ithas been extended to a larger radius. In the position shown, alllaminations have been extended to make a small air gap. In thisposition, a high permeability path exists through the pole pair 1-5 andback around through the peripheral area of the field core structure. Itis to be noticed that not all laminations are extended to the fullperiphery of the rotor. Imagine removing the rotor and looking down uponthe end of the rotor as suggested by the section line 2-2. The view seenis shown in FIGURE 2. It is seen that the central laminations extendover a 45 sector While the outer laminations extend over a lessersector, the number of laminations decreasing for each sector as oneproceeds outward. As each extended sector passes over a pole piece, thepermeability of the path increases linearly until the entire pole iscovered and would remain constant until the sector started to uncoverthe pole piece. However, as the shaft is turned the arrangement showncauses the permeability to increase by a series of straight linesegments which vary in slope because the number of laminations for agiven sector is varied, so that the actual permeability approximates asine wave as shown in FIG- URE 3.

By varying the sectors and the number of laminations in each, the sinewave can be approximated to any desired degree of perfection. Theassembled rotor can further be shaped as by grinding to even furtherimprove the shape of the permeability vs. shaft. angle plot as desired.

It is obvious that the voltage induced in the secondary windings willfollow the shape of the permeability vs. shaft angle shape identically.With all the secondary coils pairs 12, 14, 16, and 18 connected inseries as shown, all these individual voltages are automatically addedso that again, assuming all solenoids pairs to be identical e =Ke sin asin wt-l-Ke sin (ot1r/2) sin (wt1r/2) which is equivalent to e =Ke Sin(wt-j-Zot) It is obvious that by adding more poles to the field andreducing the largest sector of the rotor that this provides a device inwhich:

e =Ke sin (wt-14m) where n is any integer and K is a design constant.

In FIGURE 4, a version of this same resolver is shown which has beenarranged to measure linear rather than angular displacements in terms ofphase angle. The eight pole circular stator is replaced by the linearstator 28. The same type of windings are applied vto these pole piecesas were specified for the device of FIGURE 1. The windings include setsof primary and secondary windings and are energized in a manner similarto that of the FIGURE 1 device by means of quadrature voltage sources20' and 22'. As exemplified in FIGURE 4, source 20' is connected to theprimary windings of every other set of transverse poles and source 22'is connected to the remaining primary windings. This connection producesa linearly moving magnetic field in the same manner as the FIGURE 1system produces a rotating magnetic field. The secondary windings arealso connected in series to produce an output voltage e which varies inphase according to the linear position of the core section 30 within theair gap between the transverse poles. The shaped rotor is replaced by amovable core section 30, shaped by varying the length of the laminationsas shown by the half section 5-5. The theory of operation of this deviceis identical to that just described in connection with FIGURES 1 through3. By direct analogy it is clear that this device will produce an outputvoltage 2,, whose phase with respect to the excitation voltage which isdirectly proportional to the linear displacement of the movable coresection.

While the invention has been described with reference to specificembodiments thereof, it is contemplated that various modifications tothese embodiments may occur to those skilled in the art which do notdepart from the spirit and scope of the invention. For a definition ofthe invention reference should be had to the appended claims.

I claim:

1. Displacement measuring apparatus comprising a plurality of pairs ofopposed salient poles, each of the poles in the pairs facing one anotherbut spaced apart to define a gap therebetween, a body of magneticmaterial, means for permitting relative motion of the body with respectto the pole pairs in the gaps formed thereby, primary winding meansdisposed on at least one of the poles in each of the pairs, secondarywinding means disposed on at least one of the poles in each of the pairsto be linked magnetically with the primary winding means of the pair toa degree dependent upon the orientation of the body between the poles ofthe pair, supply means for exciting each of the primary winding meanswith a voltage which is phase-shifted from the adjacent pole pairwinding means by a predetermined electrical angle, and means connectingthe secondary winding means in series relation to provide an outputvoltage which varies in phase according to the displacement of said bodyrelative to the pole pairs.

2. Displacement measuring apparatus comprising a closed magneticstructure defining a plurality of spaced salient magnetic polesextending toward a transversely opposite portion of the structure butseparated therefrom by an air gap, a body of magnetic material adaptedfor displacement through the gaps between the poles and the transverselyopposite portion, a primary and a secondary winding disposed on each ofthe poles and being magnetically linked to a degree depending upon theorientation of the displaceable body in the gap adjacent the pole, meansfor exciting each of the primary windings with a voltage which isphase-shifted from the voltage in the adjacent primary by apredetermined electrical angle, and means connecting the secondaryWinding means in series relation to provide an output voltage whichvaries in phase according to the displacement of said body relative tothe poles.

3. Resolver apparatus comprising a generally annular stator of magneticmaterial having formed therein a plurality of inwardly extending salientpoles, the poles being circularly disposed about a central axis to forma plurality of diametrically opposed pairs of poles each having an airgap therebetween, a rotor of magnetic material having diametricallyopposed salient poles portions and mounted centrally to the stator androtatable about an axis to selectively occupy the gap between the pairsof diametrically opposite poles, a primary winding disposed on at leastone pole of each of the pole pairs, a secondary winding disposed on atleast one pole of each of the pole pairs to be magnetically linked withthe primary winding of the pole pair to a degree dependent upon theangular position of the rotor between the poles of the pair, means forexciting each of the primary windings with a voltage of fixed amplitudebut phase-shifted from the voltage on the adjacent primary winding by apredetermined electrical angle, and means connecting the secondarywinding means in series relation to provide an output voltage whichvaries in phase according to the displacement of said body relative tothe pole pairs.

4. Apparatus as defined in claim 3 wherein four pairs of opposing polesare formed symmetrically about the stator and the predeterminedelectrical angle is 90 degrees.

5. Apparatus as defined in claim 3 wherein the rotor is constructed ofan axial stack of laminations, each lamination having two diametricallyopposite salient pole portions co-diametric with the correspondingportions of the other laminations, the circumferential dimensions of thepole portions being axially graduated thereby to present areas to eachof the poles of the pair adjacent the rotor which vary approximatelysinusoidally with angular displacement of the rotor.

6. Multi-speed resolver apparatus comprising a generally annular statorof magnetic material and having a central axis of symmetry, a pluralityof diametrically opposing pairs of inwardly extending salient polessymmetrically formed on the stator about the axis thereof, the poles ofeach of the pairs being radially spaced to form a gap therebetween, arotor of magnetic material having two opposite salient poles and beingrotatable about the axis to occupy positions between the poles of saidpairs, a primary and a secondary winding disposed on each of the statorpoles, means for producing a reference voltage and a second voltage inquadrature therewith, means for connecting the reference voltage in analternatingly opposite phase relation to the primary windings of the oddpairs of stator poles, and means for connecting the second voltage inalternatingly opposite phase relation to the primary windings of theeven pairs of stator poles.

7. Apparatus as defined in claim 6 wherein the rotor is constructed of astack of laminations, each lamination having diametrically oppositesalient pole portions, the circumferential dimensions of the poleportions of the laminations being axially graduated thereby to presentto the adjacent stator poles a circumferential area which variesapproximately sinusoidally with angular displacement of the rot-or.

8. Linear displacement sensing apparatus comprising a stator of magneticmaterial having formed thereon a plurality of linearly disposed pairs ofsalient poles, the poles of each of the pairs extending toward oneanother but separated by a gap, a member of magnetic material disposedbetween the poles of said pairs and displaceable linearly with respectto the pairs, a primary and a secondary winding disposed on each of thepoles, means for pro ducing a reference voltage and a second voltage inquadrature therewith, means for connecting the reference voltwindings ofodd pairs of poles, and means for connecting age in alternatinglyopposite phase relation to the primary the second voltage inalternatingly opposite phase relation to the primary windings of evenpairs of poles.

9. Apparatus as defined in claim 3 wherein the displaceable member isconstructed of a stack of laminations, the linear dimension of thelaminations being graduated thereby to present an area to each of thefaces of the pole pairs adjacent the member which varies approximatelysinusoidally with linear displacement of the member with respect to thepole pairs.

References (Iited by the Examiner UNITED STATES PATENTS 2,427,213 9/1947Jewell 323 2,882,484 4/1959 Swainson 323-51 2,941,140 6/1960 Rudolf etal. 32351 2,996,688 8/1961 Boyd 3239O X 3,001,127 9/1961 Pitches et al323-90 3,045,196 7/1962 Packard 336 JOHN F. COUCH, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner.

W. E. RAY, Assistant Examiner.

2. DISPLACEMENT MEASURING APPARATUS COMPRISING A CLOSED MAGNETICSTRUCTURE DEFINING A PLURALITY OF SPACED SALIENT MAGNETIC POLESEXTENDING TOWARD A TRANSVERSELY OPPOSITE PORTION OF THE STRUCTURE BUTSEPARATED THEREFROM BY AN AIR GAP, A BODY OF MAGNETIC MATERIAL ADAPTEDFOR DISPLACEMENT THROUGH THE GAPS BETWEEN THE POLES AND THE TRANSVERSELYOPPOSITE PORTION, A PRIMARY AND A SECONDARY WINDING DISPOSED ON EACH OFTHE POLES AND BEING MAGNETICALLY LINKED TO A DEGREE DEPENDING UPON THEORIENTATION OF THE DISPLACEABLE BODY IN THE GAP ADJACENT THE POLE, MEANSFOR EXCITING EACH OF THE PRIMARY WINDINGS WITH A VOLTAGE WHICH ISPHASE-SHIFTED FROM THE VOLTAGE IN THE ADJACENT PRIMARY BY APREDETERMINED ELECTRICAL ANGLE, AND MEANS CONNECTING THE SECONDARYWINDING MEANS IN SERIES RELATION TO PROVIDE AN OUTPUT VOLTAGE WHICHVARIES IN PHASE ACCORDING TO THE DISPLACEMENT OF SAID BODY RELATIVE TOTHE POLES.